Silva (33-6) hasn't fought since December, when the Brazilian star shattered his left shin in a bout with Chris Weidman.

The 39-year-old Silva had won 16 straight fights and made 10 consecutive title defenses before back-to-back losses to Weidman, who took the middleweight belt from Silva in July 2013. Silva refused to retire after his gruesome injury, instead working toward a comeback.

The popular Diaz (26-9) is a former Strikeforce welterweight champion, but he has lost both of his UFC title shots. Diaz has fought just once since February 2012, losing a decision to former UFC welterweight champion Georges St. Pierre last year.